Aortic collagen and elastin synthesis will be measured at various time periods during progression of experimental atherosclerosis in rabbits. Pathobiochemical changes will be measured at the same time periods to determine whether they precede or succeed the connective tissue changes. In all cases control rabbits will also be studied. The synthesis of collagen and elastin in vessels subjected to different degrees of mean pressure and pulsatile ditention will also be measured to determine whether these physical factors are related to metabolism of the blood vessel wall and the development of atherosclerosis.